1. Technical Field of the Invention
The present invention relates generally to a magnetoresistive head which may be employed in a magnetic recording/reproducing device such as a magnetic disc unit.
2. Background Art
Recently, metal thin film discs exhibiting high coercive force, high residual magnetic flux density, and low noise properties have been developed. In addition, magnetic heads such as a metal-in gap head, a thin film head, or a laminated type magnetic head formed with laminated metal magnetic films, have also been developed These magnetic heads all utilize the electromagnetic induction, and thus their reproduced outputs vary in proportional to a relative speed between the magnetic head and the magnetic disc. Therefore, the reduction in diameter of a magnetic disc causes the reproduced output to be degraded. For avoiding this drawback, a magnetoresistive head is employed which changes its electrical resistivity on application of a magnetic field from a magnetic disc.
FIG. 8 shows a conventional shielded magnetoresistive head. This magnetoresistive head includes generally a NiFe-made magnetoresistive element (MR element) 1, FeMn-made antiferromagnetic films 2, leads 3 applying a current to the MR element, a soft magnetic film 4 providing a bias magnetic field to the MR element 1, an intermediate layer 5 magnetically insulating the MR element 1 from the soft magnetic film 4, magnetic shielding members 6 and 7, an insulating layer 8 insulating the soft magnetic film 4 from the magnetic shielding member 6, and an insulating layer 9 insulating the leads 3 from the magnetic shielding member 7.
In operation when a sense current is applied to one of the leads 3, it will flow to the MR element 1 through the antiferromagnetic films 2 and then is directed to the other of the leads 3. The sense current flowing through the MR element 1 is separated toward the soft magnetic film 4 and the intermediate layer 5 according to a resistance ratio in the MR element 1, the soft manegnetic film 4, and the intermediate layer 5. The soft magnetic film 4 and the intermediate layer 5 are usually made of material showing a greater resistivity than that of the MR element 1. Thus, most of the sense current flows through the MR element 1.
When the sense current flows through a reproducing portion 1a defined by a central portion of the MR element 1 along an easy axis of magnetization, as shown by arrow in the drawing, it will cause the soft magnetic film 4 beneath the intermediate layer 5 to be magnetized. The magnetized soft magnetic film 4 then produces a bias magnetic field acting on the MR element 1.
Additionally, when a magnetic field produced by a magnetic flux of a signal recorded on a magnetic recording medium is applied to the MR element 1 along a hard axis perpendicular to the easy axis of magnetization, it will cause the MR element 1 to be changed in electrical resistivity. This change is detected as a reproduced output voltage.
It will be thus appreciated that it is possible to detect the magnetic flux generated from the magnetic recording medium to derive the reproduced output voltage regardless of relative speed between the magnetic recording medium and the head.
The above prior art magnetoresistive head, however, has suffered from the drawback in that the increase in thickness of the MR element 1, as shown in FIG. 9, causes the reproducing portion 1a to be magnetized easily to form multi-domains. This leads to irregular displacements of magnetic domain walls due to the magnetic field of the signal from the magnetic recording medium, causing the frequency of the Barkhausen noise appearing on the reproduced waveform to be increased undesirably. Conversely, the decrease in thickness of the MR element 1 alleviates this problem, but however, it causes, as shown in FIG. 10, the MR ratio to be reduced, resulting in the reproduced output voltage being lowered.